When I showed up in the Emergency Department with textbook heart attack symptoms – chest pain, nausea, sweating, and pain radiating down my left arm – the hospital staff snapped to work and immediately ordered a flurry of tests. These included an EKG, blood tests, chest x-ray and a treadmill stress test. But all test results came back “normal”. I was then told that I was in the “right demographic” for acid reflux before being sent home – less than five hours after the onset of symptoms.

I left hospital that morning feeling terribly embarrassed for having made such a fuss over just a little case of indigestion. It was only much later – after finally being correctly diagnosed, taken directly from the E.R. to O.R. and admitted to the cardiac care unit for a myocardial infarction (heart attack)caused by a fully occluded Left Anterior Descending coronary artery – when I learned that my “normal” blood tests may have been “normal” that day because I had been sent home too soon.

This is the part of my story where I like to repeat another story – this one told to me by a woman in one of my heart health presentation audiences recently. She described being an E.R. patient herself, and overhearing a conversation between the E.R. physician and the (male) patient lying in the bed next to her, behind the cubicle curtain. She heard the doctor telling the (male) patient:

“Your EKG is fine, and your blood tests are fine, too. But we’re going to keep you for observation just to make sure it isn’t your heart.”

Thus yet another male patient with symptoms but inconclusive cardiac test results is kept in hospital for observation, while I and countless other females with symptoms but inconclusive cardiac test results aremisdiagnosed, patted on the head, and sent homefrom the E.R.

Turns out we’re not alone.A study published in The New England Journal of Medicine found that women presenting with cardiac symptoms were seven times more likely to be misdiagnosed and sent home from Emergency compared to their male counterparts.*

Here’s why that’s an important issue. The blood tests mentioned look for cardiac enzymes in the bloodstream. This test will usually be ordered when a person like me with a suspected heart attack first comes into the Emergency Department. The blood test is usually repeated two more times over the next 12 hours.

One of these tests is for a specific cardiac biomarker called troponin – particularly one called troponin I. Doctors like testing for cardiac troponin I because it’s very sensitive in detecting heart muscle damage that occurs during a myocardial infarction. The more severe the heart attack, the higher the blood levels of the troponins will be. Carolyn’s NOTE: although some consider the presence of this biomarker to be uniquely heart attack-related, increased blood concentrations of troponin are also sometimes detected in non-cardiac conditions (e.g. sepsis, hypovolemia, pulmonary embolism, or renal failure). Some marathon runners or other extreme endurance athletes are even known to have temporarily detectable troponin levels in their blood. As Dr. Malissa Wood explained in a Runner’s Worldinterview, this is because their cell membranes may leak troponin, which is what cardiac muscle does when under extreme stress. Dr. Wood (who is the co-director of the Women’s Health Heart Center at Massachusetts General Hospital, teaches at Harvard, and has run many marathons herself), cites studies showing that the healthy heart (unlike the unhealthy heart in the throes of myocardial infarction – heart attack) can quickly repair these cell membranes, stem the troponin leakage, and suffer no permanent damage.

Many patients who experience a heart attack have increased troponin levels within six hours following the onset of symptoms. According to a 2006 report* in the journal, Annals of Emergency Medicine:

“If the time of symptom onset is unknown, unreliable, or more consistent with pre-infarctional angina, then time of symptom onset should be referenced to the time of Emergency Department presentation.

“The serial measurements of the cardiac troponins over an 8 to 12 hour period of observation is supported by several studies as a reliable method of identifying and excluding acute myocardial infarction.

“When measured from time of symptom onset, sensitivities of the troponins for acute myocardial infarction improve in an incremental fashion and exceed 90% by 8 hours of symptom onset and approach 100% by 12 hours.”

This means that after 12 hours, almost everyone who has had a heart attack will exhibit raised troponin levels. It also means that under six hours is not long enough in most cases to identify or exclude heart attack.

Troponin I has two notable peaks, initially peaking between 15-24 hours after an MI, and then hitting a lower peak after about 6o-80 hours. Troponin levels may also remain high for up to two weeks after a heart attack strikes.

Cardiac troponin levels are normally so low they cannot be detected with most blood tests, so when they are detected, it’s usually significant in showing that heart muscle damage due to a myocardial infarction has indeed occurred. Test results are considered normal if the results are:

Troponin I : less than 10 µg/L

Troponin T : 0–0.1 µg/L

Normal troponin results at 12 hours after the onset of symptoms typically mean that a heart attack is unlikely.

But I was already back home from the Emergency Department within five hours – several hours before that initial 15-24 hour troponin I level would have peaked. No wonder it was “normal”.

Troponinis a complex of three proteins, two of which have particular importance in detecting heart muscle damage: troponin I and troponin T. These proteins are released into the bloodstream when the heart muscle has been damaged, typically during a heart attack. The more damage there is to the heart, the greater the amount of troponin I and T there will be in the blood.

Troponin I is thought to be a far more specific marker of cardiac damage than troponin T. Cardiac troponin T levels rise 2-6 hours after the MI and remain elevated. Both proteins return to the normal range about seven days after a heart attack.

In 2006, the European Society of Cardiology and American College of Cardiology redefined acute myocardial infarction to be predicated on the finding of increased concentrations of cardiac troponin; these and other clinical practice guidelines have led to a steady decline in the use of other cardiac enzyme blood tests like CK-MB and myoglobin as diagnostic tools to identify cardiac markers during heart attack.

Here’s a crash course in other types of blood tests for cardiac enzymes:

CK (Creatine kinase) – This is an enzyme that’s also considered to be a sensitive and specific marker for myocardial infarction, particularly in what’s known as itsCK-MBform. Its value changes in 3-4 hours after an MI, peaking in 10–24 hours. The normal value is restored within 72 hours. Because of this short duration, CK testing cannot be used for late diagnosis of acute MI. And CK-MB levels can also rise in conditions like renal failure or skeletal muscle damage such as in muscular dystrophy or a crush injury, so cannot definitively identify heart attack.

Myoglobin – Levels of the biomarker myoglobin start to rise within 2-3 hours of a heart attack or other muscle injury, reach their highest levels within 8-12 hours, and generally fall back to normal within one day. An increase in myoglobin is detectable sooner than troponin, but like CK, it is not as specific for heart damage. Blood levels of myoglobin, for example, can rise very quickly with severe muscle injury or kidney damage.

AST(Aspartate transaminase) – AST appears in the heart, liver, skeletal muscles, kidneys, pancreas, and to a lesser extent in red blood cells. A high correlation exists between MI and elevated AST levels, but this enzyme also has what’s known as low organ specificity. Translated into English, this means that the test doesn’t differentiate between high AST caused by acute MI and the liver congestion caused by strenuous exercise or muscle damage caused by intramuscular injections which can also raise AST. For example, a study** reported in the American Journal of Clinical Pathology tested for cardiac enzymes of runners competing in the 2001 Boston Marathon and found “a statistically significant increase in the values for AST” in over 30% of the marathoners tested immediately after the race ended, then four hours later and again after 24 hours post-run. This elevation was blamed on “leakage from skeletal muscle”.

22 Responses to “Those curious cardiac enzymes”

Hi Georgia,
Yes. According to Medtronic, one of the world’s largest manufacturers of pacemakers: “A pacemaker is not a cure. It will not prevent or stop heart disease, nor will it prevent heart attacks.”

How long after this happened did you actually get admitted to the OR and diagnosed as having a heart attack? Yesterday I went into the ER for the exact same symptoms and they sent me home right away too with the SAME diagnosis. It didn’t feel like it was Acid Reflux related…. and I still had chest tightness the rest of the night. I have some today, but not as bad. I just want to know if I should be looking further into this. I have a follow up with my Primary doctor next Thursday. I’m wondering how long it took you to get that diagnosis and if I should be still worried or watching it since it was less than 24 hours ago, or if you went in again later that night within a 12 hour period.

Hello Tia,
I was sent home from the ER and did not return for TWO WEEKS (a very bad decision on my part, by the way – I was so embarrassed for having made a big fuss over “nothing” – plus I’d been told very clearly by a man with the letters MD after his name: “It is NOT your heart!”) So no way was I going to go back just to be embarrassed again – until my increasingly debilitating cardiac symptoms got so bad I couldn’t even walk five steps. What I SHOULD have done was to go back the minute the same symptoms returned.

Do not be like me. If your symptoms return, seek immediate medical help. Good luck at your doctor’s follow-up visit.

Reblogged this on Mama Panda Chismis and commented:These are good to learn about especially if you are concerned about having a heart attack. ERs are releasing people too soon or are not explaining things, so educate yourself.

Nice article. I’m curious to know why the protocol has such a long time between tests.

When I went to the ER with obvious symptoms, my blood tests and ECG were normal. They convinced me to stay so they could test my blood 6 hours later (turned out to be 7 hours). The second test confirmed a heart attack. My questions are (1) how much was my heart damaged in those 7 hours (2) why wait so long between tests? They start the 6-hour timer at the the time of the first test, as if the heart attack happened at that time. If the heart attack started 2 hours before the first test, a second test would be positive long before 6 hours passes. Seems like a dangerous protocol. Why not test every hour? Yes, it costs money. But,this is the heart we’re dealing with. Rant over.

Mike, I’m not a physician – your cardiologist is your best resource for these questions. But my understanding is that it’s all about time needed before cardiac enzymes indicating heart muscle damage are detectable in the blood. The ER could test for cardiac enzymes every hour on the hour, but it takes a certain amount of time for enzymes like troponin to even appear in the bloodstream at all. A second test MIGHT be “positive long before six hours passes” but evidence suggests it’s not more likely to confirm the sooner you retest.

Diagnostic testing is NOT consistent from hospital to hospital despite diagnostic/treatment protocols. For example, I was back home within five hours of the onset of my textbook MI symptoms – far too early to see elevated enzymes in blood test results in my two back-to-back tests one hour apart, both “normal” (and this timing was NOT in line with treatment protocols, of course, which normally recommend 12 hours of observation to rule out MI when patients present with clear cardiac signs).

How much was your heart muscle damaged in those seven hours? Impossible to say, although the higher your troponin numbers, the higher the likelihood of muscle damage. If your ejection fraction numbers now appear normal, chances are your muscle damage was minimal.

A physician told me that hospital protocols can vary. At her hospital, troponins are drawn 3 times, every 8 hours. At the minimum, troponins should be done twice from 6 to 8 hours apart. This gives an opportunity to see if there are rising values. Now that I know this, I would insist on the 2 or 3 times protocol.

ERs have a “person can only be in the ER 23 hours” by insurance. Anything more requires hospital admission. This may drive the “get em out” quickly if the person looks like they don’t fit the profile.

I will add as well, that patients are also eager to leave, as lying in an ER for 23 hours is tedious, hard to sleep and certainly no TV to while away the hours. It’s an ordeal. That may drive the patients to choose to leave prematurely, particularly if they are being told they “probably” don’t have an MI problem, and instead it’s GI or anxiety. This also makes it hard for the patient to return (emotionally speaking) and worried about being perceived as imagining things.

Hi Mary – all excellent points. That’s quite the variation in E.R. protocol, isn’t it? A common practice, I’ve been told, is to do cardiac enzyme blood tests at 4 and 6 hours after admission. Or 3x q8h. Or 2x 6 and 8 hours after admission. Good grief….

There’s a confusing message in that time is heart muscle and that clarity of diagnosis takes time when the EKG and other earlier signs are within normal. Once again the importance of advocating for oneself to know that there needs to be follow up testing/observation for women as well as men.

Thanks for providing the rationale for those with concerns to insist on necessary observation. You are an advocate through cyberspace who provides us with ways to advocate for ourselves.

Thank you for your comment, Dina. You raise an important point. For example, had I known more about these blood tests at the time, I could have requested a follow-up test later that day. Staff could have actually discharged me and just had me return later – no need to even take up a bed in the E.R all day! Anything would have been better than sending a patient presenting with textbook heart attack symptoms home with a GERD misdiagnosis.

I was told for months that my symptoms were not related to my heart, despite the fact that I could no longer walk around the block, play badminton, was in a nauseous state etc. I had been to see four different doctors, three heart, pulmonary, renal, etc. I too passed treadmill testing. On the morning that I again called my heart doctor begging for help, the message was: You have no stenosis! I am sending you back to the Pulmonary doctor.

I decided at 12 midnight to drive myself to the hospital. I made copies of all my medical records, had a flat tire on the way, which could not be fixed, found a man pulling out of the last emergency parking space and into the hospital I took myself to. Lo and Behold.

The doctors on duty knew it was my heart. A 98% blockage in the main artery. While waiting overnight, I had a very unpleasant experience in that I was given an overdose of NitroGlycerine; no one on duty could hear me calling for help, the monitor was not being watched. The problem: for my size and weight, the dose was too strong.

I thought what I experienced was the big bang and away you go. The symptoms were classic for someone having heart problems. A friend with a Hollywood Doctor in NYC just had a quintuple byass operation; his doctor was hearing for months of the same symptoms and fluffed it off.

The problem: today’s doctors do not know or recognize the typical symptoms of heart disease. These symptoms are typical. They rely on stress test (most pass these) and I could go on and on. Many of us are dead or dying because the doctors are ignorant of typical signs of heart trouble Stop relying on stress testing. Do the right thing: “Angiogram!! What is the difference if it is risky? Which is worse, dying with blocked arteries or complications from the procedure? At least you are in the hospital and they can try to save your life.

Yikes – what a story, Tully (including the bits about driving yourself to hospital at midnight, getting a flat tire, snagging the last available parking space, that overdose of nitro – WOW!!) For some patients (the estimate is as high as 20%), treadmill stress tests may not necessarily be accurate in identifying cardiac issues. Personally, I’m skeptical that angiography will ever become the default diagnostic test to rule out heart attack (it’s not only invasive and risky, but very expensive and less accurate at diagnosing certain microvascular or spasm disorders of the coronary arteries). In the past several years, we’ve also seen distressing examples of “stent-happy” cardiologists implanting unnecessary stents inappropriately in patients whose symptoms could have been more effectively (and safely) managed with cardiac meds.

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♥ The first WomenHeart Support Group program in Canada is being held at Royal Jubilee Hospital in Victoria, BC on the third Wednesday evening of each month. Any woman living with heart disease is invited to attend. For more info, contact WH-BritishColumbia@womenheart.org